The present invention relates to a method for measuring an unknown parameter of a thin film, such as a refractive index, absorption coefficient, and film thickness, and more particularly to a method for measuring an unknown parameter, such as a refractive index, absorption coefficient, and film thickness, of the uppermost thin film of a multi-layered film.
The ellipsometry has been known as a noncontact and nondestructive method for measuring the refractive index. This method, however, requires a complicated and huge apparatus.
U.S. Pat. application Ser. Nos. 07/256,911 and 7/453,902, which were invented by the same inventor as that of the present patent application, discloses a novel method for measuring the refractive index of a thin film layer. In this method, P-polarized monochromatic light and S-polarized monochromatic light are made to enter the thin film whose refractive index is to be measured, reflectances for them are measured, and a refractive index of the thin film is mathematically worked out by using the results of the measurements.
The application of the above methods, however, is limited only to the thin film that is transparent to the wavelength of the used light, and further is applicable for a single layer thin film structure alone.